An unknown element "X" has electron configuration ["Ar"]3d^5 and a charge of 3+. What is the atomic number of "X"?
1 Answer
Explanation:
For starters, you know that your element is located in period
This means that you can write the noble-gas shorthand configuration for this unknown element, let's say
"X"^(3+): ["Ar"] 3d^5
Now, the trick here is to realize that when a transition metal located in period
In other words, when the
So when
You can thus backtrack and add electrons to the
"X"^(2+) = "X"^(3+) + "e"^(-)
This means that you have--remember, the third electron was removed from the
"X"^(2+): ["Ar"] 3d^6
Next, you have
"X" = "X"^(2+) + 2"e"^(-)
This means that you have--the first two electrons were removed from the
"X": ["Ar"]3d^6 4s^2
Therefore, you can say that a neutral atom of
overbrace("18 e"^(-))^(color(blue)("the same as neutral atom of Ar")) + overbrace("6 e"^(-))^(color(blue)("in the 3d orbitals")) + overbrace("2 e"^(-))^(color(blue)("in the 4s orbitals")) = "26 e"^(-)
This implies that a neutral atom of
You can conclude that your unknown element is iron,